Functional Region-Based Design Rules for Stress-Aligned Multi-Axis Fused-Filament Fabrication

Multi-axis fused-filament fabrication (FFF) expands the design space of polymer components by enabling spatially oriented filament paths. Existing stress-aligned deposition methods can align paths with principal stress directions, but they provide limited guidance for selecting local deposition strategies in mechanically critical regions where loads are introduced, transmitted, redirected, supported, or constrained. This paper proposes a functional region-based method for deriving reusable local deposition-design rules. The method identifies the local structural context and governing load-transfer mechanism in a representative bolted bracket and abstracts these regions into compression, open-hole tensile, and bearing-response benchmarks. The compression benchmark is evaluated experimentally. Candidate deposition strategies for the open-hole tensile and bearing-response benchmarks undergo qualitative comparative screening using an FEM model with the Tsai-Wu failure-initiation index. Selected configurations are further evaluated through physical testing on multi-axis FFF specimens. The physical tests show that continuous load-transmitting paths are favorable in the investigated open-hole and bearing-response cases, whereas adding local offset reinforcement did not automatically improve the tested configurations. The resulting deposition-design rules were applied to a representative load-bearing bracket, which reached 3.89 kN and provided component-level transfer-feasibility evidence under the investigated conditions.